As others have mentioned, Dalaran performance is all about your system RAM. I hardware box, and one machine has only 2gb of ram -- it takes a very long time to zone into Dal. The rest are all 4gb+ and zone in very quickly. The video card doesn't seem to make much difference here, on of my boxes has only 32gb video ram but with 4gb system ram it's just fine in Dal.

I used to box on a single machine pre-wrath, and upgraded from 4gb to 12gb due to continued fail at the Aldor rise elevator boss -- even with 5 instances running 12gb made all the difference. (This requires a 64-bit OS of course, I'm on Macs).